Trapping ions at high temperatures: thermal decay of C60 +

An ensemble of trapped C₆₀ ⁺ ions has been heated with a continuous CO₂ laser to a stationary state where, in time average, the same energy is emitted as absorbed. With 10 W laser power, equilibria have been reached, which correspond to temperatures between 1800 and 2000 K. The ions are confined in a radio frequency quadrupole field created by a set of ring electrodes (split ring electrode trap). The number of stored ions can be determined in two ways, on one side by extracting and counting them with a Daly detector, on the other side via imaging their thermal emission onto an intensified CCD camera. Single photon sensitivity and a spatial resolution of a few μm provide precise information on the geometrical distribution and the total number of the trapped C₆₀ ⁺ ions. The spectral distribution of the emitted photons or their total number provides information on the internal energy of the ions. Trapping times of many minutes make it possible to follow very slow thermal loss of C₂ from hot C₆₀ ⁺ resulting in fragmentation rates between 10^?1 and 10^?3 s^?1. Correlating them to the internal temperature leads to a curved Arrhenius plot. The resulting parameters are smaller than the values derived from nonequilibrium ensembles.     

Formation of fullerene dianions in a Penning trap

Fullerene dianions in the range C₇₀^2- to C₉₀^2- have been created by subjecting trapped fullerene monoanions to low energy electrons in a Penning trap. The dianion production was found to be a function of the trapping-potential depth and the time of interaction between the simultaneously stored monoanions and electrons. Under similar conditions the dianion yield depends on the size of the fullerenes with more than 10% of the trapped C₉₀^- ions forming dianions while the corresponding relative yield for C₇₀^2- was less than 0.1%. The large difference can be explained by the repulsive Coulomb barrier and the second electron affinity of the fullerenes.     

Effect of N 2 + ion implantation on the electrochemical corrosion behaviour of Fe−Ni alloy in. 1N H2SO4 solution

A three sweep potentiokinetic technique was employed to study the electrochemical corrosion behaviour of Fe-50 at % Ni in .1N H₂SO₄ solution. The as received foil did not show any passivation but it was observed in case of Fe?Ni samples implanted with N₂ ⁺ ions at an energy of 100keV. Also it was seen that the primary passivation potential E_pp and the critical current density in the corrosion experiment decrease as the implanted nitrogen ion dose increases from 5*10¹⁵ to 1*10¹⁷ ions/cm². The identification of products formed during corrosion experiment has been attempted with the help of conversion electron Mössbauer spectroscopy (CEMS), X-ray diffraction (XRD) and X-ray photoemission spectroscopic (XPS) techniques, and the possible mechanism of reactions is discussed with reference to their results.     

Elektronenausbeute bei Lithium-Ionenbeschuß von Bildwandlerflächen

The electron yield in the case of bombardment of a V2A type stainless steel plate by Li⁺ ions with energies between 20 and 80 keV was measured. The yield is increasing from 2·5 electrons per ion for 20keV to 4 for 70 keV. The electron yield in case of transmission by Li⁺ ions (number of electrons emitted on the back side of the foil per incident ion) of thin carbon foils with a layer of evaporated silver was measured. For this purpose the electrons emitted on the foil back side are accelerated in an immersion objective lens, and the resulting crossover of the beam is focussed into a Faraday cage by a projector lens. The electron yield depends on the ion energy and the foil thickness. Its value lies between 1 for a 1050 AU thick silver foil and 40 keV and 4 for a 380 AU thick silver foil and 80 keV. The range of Li⁺ ions in silver can be estimated by extrapolation of the yield curves. It is increasing from 600 AU for 10 keV to 2300 AU for 80 keV. The electron yield may not be characteristic for the target material since in a vacuum of 10^?4Torr the formation of a thin layer of polymerized hydrocarbon on the surface must be expected.     

Kinetics of luminescence induced by sputtering metallic cadmium by a pulsed fast electron beam in helium

Results of an experimental study of the kinetics of luminescence observed when a metallic cadmium foil is bombarded in a helium medium by a 3-ns pulsed beam of 150-keV fast electrons are reported. The foil was irradiated at gas pressures from 76 to 2280 Torr. At a foil temperature of T = 240° C, the de-excitation time of the Beitler levels of the Cd II ion was measured as a function of the buffer gas pressure and the constant of collision quenching of the 5s22D_5/2 level of Cd II by He atoms was determined as k ≈ 3 × 10^-29 cm⁶/s. The experimental data were compared with calculations performed for the gas—vapor mixture in order to find the fraction of excited Cd II ions in the 5s²2D_5/2 state produced directly as a result of sputtering of metallic cadmium by high-energy electrons and by components of the helium plasma. At a helium buffer gas pressure of P ≤ 2.5 atm and a temperature of the cadmium target of T = 240° C, the value of this quantity was found to be α = 0.28 + 0.23P (where P is the helium pressure in atmospheres).     

On the sensitivity of ion traps for spectroscopic applications

Ba⁺ ions, created by surface ionization near one endcap of an rf quadrupole trap were slowed down by collisions with the background gas. At He pressures of 10^?6 mbar or more 2% of the primary ions could be trapped. The sensitivity of ion detection by fluorescence radiation allows spectroscopic experiments, starting from less than 10⁷ particles. The observation of the ground-state hyperfine splitting of¹³⁷Ba⁺ is given as an example.     

Laser-triggered quasi-monoenergetic ion beams at a moderate intensity and pulse duration

Plasma produced by short laser pulses from thin homogeneous foils with light and heavy ions is capable of generating quasi-monoenergetic light ions. This happens for the tail of light ions near the front of heavy ions. It was found that this effect is well pronounced for a moderate laser intensity (～10¹⁸ W/cm²) and pulse duration (～1 ps) by using a 2D particle-in-cell simulation of the laser interaction with thin CD₂ foils. Quasi-monoenergetic deuterons form a jet from the rear side of the foil with the energy ～1 MeV. The conversion efficiency to these quasi-monoenergetic ions is 10^?3.     

Independent UHF plasma source and possibility of filling open magnetic trap

A stationary UHF plasma source, its characteristics and possibility of filling open magnetic trap with plasma injected from it have been described. Plasma is created in the source at frequency of 2400 MHz (supplied power is up to 150 W) in the electron cyclotron resonance (ECR) regime under working gas pressure 10^–5–10^–2 Torr. By changing discharge conditions one can change the injected plasma density from 10⁹ to 10¹² cm^–3, at the temperatureT _e=2–10 eV. The possibility of efficient plasma injection from the source into the open magnetic trap of various configurations is shown experimentally. Plasma characteristics in the trap are presented under various experimental conditions. It is established that plasma parameters can be easily changed in the trap.     

Molecular effect in the formation of the energy spectrum upon the transmission of low-energy hydrogen ions through ultrathin carbon foils

The energy spectra of ions transmitted through ultrathin diamond-like foils irradiated by H⁺, H⁺₂, and H⁺₃ ions with energies from 2 to 12 keV/nucleon are studied. For molecular ions incident on the target with identical velocities, a considerable broadening of the energy spectrum is observed with an increase in the ion mass. The spectrum halfwidth reduced to the identical particle velocity remains constant for each type of incident ion, irrespective of the foil thickness.     

Frequency response measurement of high-speed photodetectors using the spectrum power method in a delay self-heterodyne system

We report on a photoionization scheme for controlled loading of ⁸⁸Sr⁺ ions into a radio-frequency (rf) ion trap. The two-step doubly-resonant process drives the ⁸⁸Sr atom on the 5s^{2 1} S ₀ – 5s5p¹ P ₁ transition at 461 nm using a frequency-doubled diode laser, and then excites the atom to the autoionizing (4d²+5p²) ¹ D ₂ state with 405 nm light from a free-running diode laser. This method of trap loading is quantitatively compared to electron bombardment loading, and shown to reduce the Sr vapour pressure required to load by four orders of magnitude. It also provides more than an order of magnitude reduction in the day-to-day variation of the voltages required to compensate micromotion. We additionally introduce a two-step atomic source consisting of an oven and hotplate, which reduces the number of impurities evaporated towards the trap. This is shown to significantly reduce fluctuations in required micromotion compensation voltages. The demonstrated reduction in flux and increased source purity are expected to improve the reliability of trap operation for precision ion-trap experiments. PACS 32.80.Fb; 32.80.Pj; 39.10.+j     

Relative Anfangsbesetzungszahlen der Zustände 2p und 3d folienangeregter Wasserstoffatome

The Lyman-α radiation of fast moving hydrogen atoms excited by a thin carbon foil is measured using a channel electron multiplier with a Mg F₂ filter. The photonintensity-versus-distance curve exhibits the 2p (1.596 ns) decay followed by a cascade tail originating mainly from the 3d level (15.47 ns). The data is analyzed by a computer program using the known mean lives of the 2p, 3d, and 3s states and yields the relative initial state populationY=N _2p ⁰ N _{3 d} ⁰ which depends on the kind of incident ions (H⁺ or H₂ ⁺). For H₂ ⁺ ions, excited with a single foil, there might be a slight dependence ofY on the beam velocity, but for H⁺ ions incident on the foil, no such dependence is found.     

Penning trap assisted decay spectroscopy of neutron-rich 115Ru

Exotic, neutron-rich ¹¹¹Mo and ¹¹⁵Ru nuclei, produced in proton-induced fission of ²³⁸U target, were separated with the IGISOL mass separator. The separator was coupled to the JYFLTRAP Penning trap to select the ions of a single, desired element out of the isobaric IGISOL beam. Monoisotopic samples of ¹¹⁵Ru and ¹¹¹Mo ions were observed with a microchannel plate detector after the trap or were implanted on a catcher foil for gamma- and beta-ray coincidence spectroscopy. In spite of short data taking time new gamma transitions were identified in the beta decay of very neutron-rich ¹¹⁵Ru.     

Temperature measurement of 6He?+? ions confined in a transparent Paul trap

The LPCTrap setup is a transparent Paul trap dedicated to the measurement of the ???C?? correlation coefficient a _?|? in the ?? decay of trapped radioactive nuclides. In a first experiment, the system has been used to record ??10⁵ coincidences between the ?? particles and recoiling ions emitted from the decay of ⁶He^?+? ions. The analysis of the collected data has already shown that the size of the ⁶He^?+? ion cloud confined in the Paul trap is a critical parameter, potentially limiting the accuracy on the a _?|? measurement. We report here the precise determination of the trapped ion cloud temperature and size. This was performed by extracting the trapped ions toward a position sensitive micro channel plate detector at different phases of the RF driving field. We find a temperature T _exp ?= 0.107(7) eV, consistent with the temperature values inferred using two other observables but 20% higher than the temperature T _sim ?= 0.09 eV predicted by realistic simulations of the ions interacting with the H₂ buffer gas.     

Photon-trap spectroscopy of size-selected free cluster ions: “direct” measurement of optical absorption of Ag+ 9

An absorption spectrum of size-selected free cluster ions has been measured “directly” via extinction of light without relying on photodepletion/dissociation spectroscopy. The novel technique employs an ion trap and an optical cavity; cluster ions stored in an ion trap interact with photons trapped in a cavity. The storage lifetime of photons in the cavity provides “direct” observation of extinction of light (photon-trap spectroscopy, which is a generalized scheme of cavity ring-down spectroscopy). The first measurement is performed on ultraviolet absorption of Ag₉ ⁺. Temperature dependence of the spectrum is presented by cooling the ion trap down to 10 K.     

Optical detection of Yb+ trapped in an rf trap

The fluorescence from Yb⁺ ions trapped in an rf trap was detected by driving the²S_1/2−²P_1/2 transition at 369.52 nm with the radiation generated by sum-frequency mixing of diode-laser and argon-ion-laser radiation. The rf resonance absorption signal as well as the fluorescence signal, when the Yb⁺ ions were continuously irradiated by the resonant uv radiation, faded out with a decay time shorter than the storage time. This observation suggests that the Yb⁺ ions disappeared from the trap with the irradiation of the resonant uv radiation.     

The study of damage and optical properties in LiNbO3 implanted by MeV Er and He ions

Abstract

Two LiNbO₃ (X and Y cut) crystals from different companies were implanted by 3.0 MeV Er ions to a dose of 7.5 × 10¹⁴ ions/cm² and 3.5 × 10¹⁴ ions/cm² with different beam current densities, respectively. After annealing at 1060°C in air for 2 hours, one LiNbO₃ sample was implanted by 1.5 MeV He ions to a dose of 1.5 × 10¹⁶ ions/cm². The Rutherford backscattering/channeling and prism coupling method have been used to study the damage and optical properties in implanted LiNbO₃. The results show: (1) the damage in LiNbO₃ created by 3.0 MeV Er ions depends strongly on the beam current density; (2) after annealing at 1060°C in air for 2 hours, a good Er doped LiNbO₃ crystal was obtained; (3) there is waveguide formation possible in this Er-doped annealed LiNbO₃ after 1.5 MeV He ion implantation. It is suggested that annealing is needed to remove the damage created by MeV Er ions before the MeV He ion implantation takes place, to realize the waveguide laser for Er doped LiNbO₃.     

Potential-induced sonoelectrochemical graphene nanosheets with vacancies as hydrogen peroxide reduction catalysts and sensors

Defective graphene nanosheets (dGN_4V) with 5-9, 5-8-5, and point defects were synthesised by a sonoelectrochemical method, where a potential of 4 V (vs. Ag/AgCl) was applied to drive the rapid intercalation of phosphate ions between the layers of the graphite foil as a working electrode. In addition to these vacancies, double vacancy defects were also created when the applied potential was increased to 8 V (dGN_8V). The defect density of dGN_8V (2406 μm⁻²) was higher than that of dGN_4V (1786 μm⁻²). Additionally, dGN_8V and dGN_4V were applied as catalysts for the hydrogen peroxide reduction reaction (HPRR). The mass activity of dGN_8V (1.31 × 10⁻² mA·μg⁻¹) was greater than that of dGN_4V (1.17 × 10⁻² mA·μg⁻¹) because of its high electrochemical surface area (ECSA, 1250.89 m²·g⁻¹) and defect density (N_D, 2406 μm⁻²), leading to low charge transfer resistance on the electrocatalytic interface. The ECSA and N_D of dGN_4V were 502.7 m²·g⁻¹ and 1786 μm⁻², respectively. Apart from its remarkable HPRR activity, the cost-effective dGN_8V catalyst also showed potential as an amperometric sensor for the determination of H₂O₂.     

Beam-foil lifetimes of highly ionized silicon

Electronically excited states of Si ions are created by passing a 20 MeV Si⁵⁺ beam through a thin carbon foil. The EUV-radiation (λ=13–61 nm) emitted by the beam is analyzed using a grazing-incidence spectrometer. From the decay curves, lifetimes of 24 low lying levels in Si VIII to Si XII and of the 4f and 5g levels of Si XI and Si XII are derived. Cascades from doubly excited states turn out to be an important contribution to the radiation observed. The lifetime values of this work are compared to theoretical data mainly of Wiese, Sinanoλu and Dankwort/Trefftz. Most experimental values agree with at least one of the theoretical values. The decay time 560 ps of the 2s2p ^{3 3} D ₃ ⁰ state of Si IX is clearly longer than the theoretical prediction (highest value 455 ps by Sinanoglu).     

Target plasma formation by UHF power

The properties of plasma injected into an open magnetic trap of uniform field from an independent UHF source have been investigated. Plasma is created in the UHF source at the frequency of 2400 MHz (power input 150 W) in the electron cyclotron resonance (ECR) regime at the pressure of neutral argon (10⁻⁵−10⁻²) torr. It is established that a rather quiescent target plasma with controlled density within the range of (2 × 10⁸−2 × 10¹²) cm⁻³ and temperature 2–3eV is accumulated in the trap. It turned out that plasma lifetime in the trap is determined by a classical mechanism of particle escape at the expense of collisions, at fixed value of magnetic field in the trap it practically is not changed with the variation of neutral gas pressure and reaches the value ≈ 4×10⁻³ s at the magnetic field strength in the trap equal 1600 Oe.     

Correlation between defect-related electroluminescence and charge trapping in Gd-implanted SiO<Subscript>2</Subscript> layers

When amorphous silica is bombarded with energetic ions, various types of defects are created as a consequence of ion-solid interaction (oxygen deficient centers (ODC), non-bridging oxygen hole centers (NBOHC), E^′-centers, etc.). Luminescent peaks from oxygen deficiency centers at 2.7 eV, non-bridging oxygen hole centers at 1.9 eV and defect centers with emission at 2.07 eV were observed by changing the concentration of implanted Gd³⁺ ions. Charge trapping in Gd-implanted SiO₂ layers was induced using constant current electron injection to study the electroluminescence intensity with dependence on the applied voltage change. The process of electron trap generation during high field carrier injection results in an increase of the electroluminescence from non-bridging oxygen hole centers. Direct correlation between electron trapping and the quenching of the electroluminescence at 2.07 eV and 2.7 eV was observed with variation of the implanted Gd concentration. PACS 78.60.i; 72.20.Jv; 78.20.-e